Such a steering system is used to steer a vehicle, for example a truck or a tractor.
The driver actuates a steering member, for example a steering wheel, which is connected to the control valve. Depending on the direction of the steering movement the control valve opens the flow path from the high pressure port to one of the working ports and another flow path from the other working port to the low pressure port. In each flow path a number of orifices or bleeds are arranged. Before entering the control valve the fluid from the high pressure port is guided through the measuring motor. The measuring motor acts on the control valve in a sense to close the above mentioned flow path when an amount of hydraulic fluid corresponding to the intended steering angle of the steering member has been delivered or metered to the respective working port.
In many cases the control valve comprises a housing having a bore in which a spool and a sleeve are positioned. The spool and the sleeve can be rotated relative to each other to open the above mentioned flow paths and to close other flow paths, if appropriate.
Such a steering system has the drawback that a change from one steering direction to the opposite steering direction shows a certain gap or dead zone. In other words, when the steering direction is changed a certain time passes before the steering motor can react to the new steering command. This makes in some cases steering difficult and uncomfortable.